1. Field of the Invention
The present invention relates to methods for manufacturing cathode assemblies of field emission displays and, more particularly, to a method for manufacturing a cathode assembly containing carbon nanotubes as electron emitters.
2. Description of Related Art
Field emission displays (FEDs) are a new, rapidly developing kind of flat panel display technology. Compared to conventional technologies, e.g., cathode-ray tube (CRT) and liquid crystal display (LCD) technologies, FEDs are superior in having a wider viewing angle, low energy consumption, smaller size, and higher quality display. In particular, carbon nanotube-based FEDs (CNTFEDs) have attracted much attention in recent years.
Carbon nanotube-based FEDs employ carbon nanotubes (CNTs) as electron emitters. Carbon nanotubes are very small tube-shaped structures essentially composed of a graphite material. That carbon nanotubes can be produced by arc discharge between graphite rods was first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes can have an extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. with length/diameter ratios potentially greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). Thus, carbon nanotubes can transmit an extremely high electrical current and have a very low electric field electron emission activation voltage (approximately 2 volts/micron). In summary, carbon nanotubes are one of the most favorable candidates for electrons emitters in electron emission devices and can play an important role in field emission display applications.
A conventional cathode assembly includes a cathode supporter and a number of carbon nanotubes used as an electron emitter. The number of carbon nanotubes are formed on the cathode supporter. Conventional methods for forming the carbon nanotubes on the cathodes supporter mainly include a mechanical method and a growing method.
The mechanical method glues the carbon nanotubes on the cathode supporter by chemical adhesive. The mechanical method is simple, but it is more difficult to operate and requires more time. Especially, if the diameter of the carbon nanotubes is less than 1 nm, the mechanical method is impossible to operate.
A conventional growing method is plating a metal catalyst on the cathode supporter, then growing carbon nanotubes directly on the cathode supporter using a chemical vapor deposition method or an arc discharge method. However, for a triode type field emission display, the metal catalyst is plated on the cathode supporter through gate holes defined between every two adjacent gate electrodes, therefore, the length of the metal catalyst is the same as the gate holes. If the carbon nanotubes are grown too high, the carbon nanotubes arranged at the periphery will contact with the gate electrodes and a short circuit takes place between a cathode electrode and the gate electrode. Furthermore, part of the electrons emitted from the carbon nanotubes will be transmitted to the gate electrode to creep and decrease the power utilization efficiency.
What is needed, therefore, is a method for manufacturing a cathode assembly of a high-performance field emission display.